Voltage control device



Nov. l5, 1960 Filed May l5, 1954 J. S. MALSBARY VOLTAGE CONTROL DEVICE 3 Sheets-Sheet 1 J. s. MALsBARY 2,960,646

VOLTAGE CONTROL DEVICE Filed May 13. 1954 3 Sheets-Sheet 2 FIGS. g o L/@2 )Q5 Nov. 15, 1960 Filed May 13, 1954 J. S. MALSBARY VOLTAGE CONTROL DEVICE 3 Sheets-Sheet 3 VOLTAGE CONTROL DEVICE .laines S. Malsbary, Glendale, Mo., assignor to Wagner Electric Corporation, St. Louis, Mo., a corporation of Delaware Filed May 13, 1954, Ser. No. 429,465

12 Claims. (Cl. 323-75) The present invention relates generally to the voltage regulator art and more particularly to a novel voltage control device by which the output voltage of a transformer can be held constant or can be varied in any desired manner regardless of limited variations of the supply voltage thereto, and which regulates said output voltage smoothly and practically instantaneously with the demand therefor.

Briey, the present invention comprises a control device in combination with a transformer, the control providing variable compensating or adjusting voltage which is superposed on either the input or the output voltage of the transformer so as to maintain the output voltage at the desired value regardless of changes in the supply voltage within predetermined limits. `In the preferred construction, the adjusting voltage is developed in a bridge circuit which includes four saturable core reactors Whose impedances are responsive to selected external conditions, the magnitude and direction of the adjusting voltage being determined by the impedance values of the arms of the bridge circuit.

At the present time, the output voltage of a transformer is usually regulated by means of a tap changing device associated with either the primary or secondary windings of the transformer, or by varying the impedance of a coil connected in one of the supply leads or in the output leads of the transformer.

The tap changing construction has the disadvantage that it requires numerous switches which are subject to arcing, and wear and tear, and a rather complicated mechanical control for operating the switches. It also results in a stepwise regulation of the Output voltage caused by abrupt changes in the connections of the afore mentioned component circuit parts. Furthermore, the best available regulation employing tap changers is in the nature of A; of 1% of normal, and the regulation is effected only after the controlled voltage has been at an abnormal value i.e., more than for an appreciable period of time.

The construction employing a variable impedance connected in series with the supply line has the disadvantage that the voltage across the primary can never be greater than the supply voltage.

Therefore, one of the objects of the present invention is to provide a voltage control device for use with a transformer whereby the output voltage of the transformer can be held substantially constant or changed to any desired value regardless of changes in the supply voltage within predetermined limits. More particularly, it is an object to provide such a device in which the load voltage can be maintained constant within 1/2 of 1% of normal when the input voltage varies between 90% and 110% of normal.

Another object of the present invention is to provide a voltage control device for regulating the output voltage of a transformer without interrupting the normal flow of power either on the primary Or secondary side of the transformer. More particularly, it is an object to provide es tet rf-tice 2,960,546 Patented Nov. `15, 1960 such a device whereby the controlled voltage is varied smoothly as distinguished from stepwise or incremen variation, and whereby the variation is substantially instantaneous with the demand therefor.

Further Objects and advantages of the present invention will be readily apparent from the following detailed description, reference being had to the accompanying drawings wherein preferred embodiments of the present invention are shown.

In the drawings:

Fig. 1 is a schematic wiring diagram of the preferred circuit construction in which a correcting winding is provided on the main transformer core,

Fig. 2 is a simplified schematic diagram of the circuit in Fig, 1, in which all four reactors are shown to be of substantially the same size, thereby diagrammatically indicating that they have about the same reactance value. In this situation, the effective adjusting voltage e is zero, and the supply voltage and the input voltage to the transformer are substantially equal,

Fig. 3 is a schematic diagram similar to Fig. 2 but in which the reactance values of two series connected reactors are unequal. In this situation, the adjusting voltage e is bucking or opposing the supply voltage,

Fig. 4 is a schematic diagram similar to Fig. 2 and Fig. 3 but in which the adjusting voltage e is shown diagrammatically as aiding the supply voltage,

Fig. 5 represents the same circuit components and connections as shown in Fig. 2 except the transformer core is shown in a vertical position,

Fig. 6 is a rst modified circuit construction wherein the correcting winding on the main transformer core (Fig. l) is replaced by the secondary winding of a separate or auxiliary transformer whose primary winding is connected across the secondary' leads of the main transformer.

Fig. 7 differs from Fig. 6 in that the primary winding of the separate or auxiliary transformer is connected across the supply line instead of across the output leads of the main transformer,

Fig. 8 is a further modified construction, wherein the adjusting voltage is superposed on the output voltage, and the correcting winding is wound around the core of the main transformer,

Fig. 9 is another modification, in which the correcting winding is located on a separate or auxiliary transformer and the primary winding of the separate transformer is connected directly across the terminals of the secondary winding of the main transformer ahead of the bridge circuit,

Fig. l0 is a modification of Fig. 9. It differs therefrom in that the primary winding of the separate transformer is connected across the secondary circuit of the main transformer on the load side of the bridge circuit,

Fig. l1 is a vector diagram showing the voltage arid current conditions in the Wheatstone bridge when the load current is cophasal with the transformer voltage, and

Figs. 12 and 13 are vector diagrams illustrating how the adjusting voltage developed in the bridge circuit adds vectorially to the supply voltage.

Referring to the drawings more particularly by refer* ence numerals, specically Fig. l, the numeral 12 indicates a conventional power transformer (shown schematically) which includes a secondary winding 14, two primary windings i6 and 18, and a correcting winding 2t) shown on the primary side but which functions as another secondary, as will be described more fully hereinafter.

Load leads 22 and 24 are connected to the secondary winding 14, and supply leads 26 and 28 are connected to the primary windings 16 and 18. The impressed supply voltage is indicated as V1 and the secondary voltage is indicated as V2.

A network circuit 30 which controls the magnitude and direction, .i.e., the phase relation, of an adjusting voltage e, comprises four saturable core reactors 32, 34, 36, `and 38 containing laminated iron cores. Each of the saturable reactors includes a D.C. winding and A.C. winding. In the description, the A.C- and D.C. windings will be referred to as 32AC, 32DC, 34AC, 34DC, and

so on.

The A.C. windings of the four reactors are connected together in a so-called Wheatstone bridge circuit, the windings 38AC and 32AC being connected together at a corner 4t), the windings 32AC and 34AC `being connected together at a corner 42, the windings 34AC and 36A() being connected together at a corner 44, and the windings 36AC and 38AC being connected together at a corner 46.

A conductor 48 connects the corner 46 with one side of the primary winding 16, and a conductor 50 connects the corner 42 with one side of the primary winding 18, thereby providing the power connection for the aforementioned bridge circuit.

The other two corners of the bridge circuit, i.e., corners 4i? and 44, are connected to the correcting winding 20 through conductors 52 and 54 respectively.

As briefly mentioned hereinabove, the impedances of the reactors in the legs of the bridge circuit are controlled so that diametrically opposite arms of the bridge have substantially the same impedance. In order to accomplish this result, the windings 38DC and 34DC are connected together in series, and are connected in series with a D.C. power source 56 and a variable resistor 57, through conductors 58 and 60.

In like manner, the windings 32DC and 36DC are connected together in series, and in series with a D.C. power source 62 through conductors 64 and 66.

Thus, it will be apparent that by adjusting the variable resistor 57, the direct current passing through the windings 38DC and 34DC can be controlled so as to simultaneously vary the A.C impedance of the reactors 38 and 34. For example if the variable resistor 57 is adjusted so that a relatively small direct current flows through the windings 38DC and 34DC, the A.C. impedance of the reactors 38 and 34 will be relatively high. On the other hand, if the direct current flowing through the windings 38DC and 34DC is relatively large, ythe A.C. impedance of the reactors 38 and 34 will be relatively low.

In like manner, the impedances of the reactors 32 and 36 can be controlled by adjusting the variable resistor 63.

Although the Variation of the impedances of the reactors 32, 34, 36 and 3S has been described as being accomplished by controlling the flow of direct current through the D.C. windings, it will be apparent from the present disclosure that the same result can be accomplished by mechanical means, as for example by physically changing the longitudinal position of an iron core mounted within'each reactor coil.

Furthermore, the impedance of the various reactors can be varied automatically responsive to any selected external condition s'uch as, for example, supply current, load current, output voltage, or the like. The preferred construction for automatically controlling the impedance of the reactors, and consequently the output of the transformer 12, is described in my copending application, Serial No. 497,978, filed March 30, 1955.

Hereafter, in the description of the operation of the device, the impedance of the various reactors will be referred to as being relatively high or relatively low, without mentioning how the change of impedance has been accomplished, i.e., whether by varying the D.C. current in the windings 34DC, 38DC and 32DC, 36DC as by adjusting the variable resistors 57 and 63, by mechanical means, or by automatically varying the current currents flowing in the reactances.

in the D.C. windings responsive to some external condition. Y

Operation As briefly mentioned hereinabove, the problem is to maintain constant, the voltage V2 across the secondary, regardless of changes within a predetermined range in the impressed supply voltage V1 across the leads 26 and 28.

The operation of the device can be described either from the standpoint of the primary winding of the transformer having a certain number of effective ampere turns, depending upon whether the ampere turns of the correcting winding are either aiding or opposing the ampere turns of the windings 16 and 18 and the extent of the liux changes it causes, or it can be described from the standpoint of having the voltage e appearing across the points 46-42 of the bridge circuit superposed on or injected into the impressed supply voltage in series aiding or opposing depending upon the relationship of the impedances of the reactors in the bridge circuit. Because of the difculty of computing the various voltages and currents when the eifective ampere turn approach is used, the other approach has been deemed to be more advantageous, and is the one which will be used.

In the following discussion, the transformers will be considered as ideal transformers, i.e., as not having any resistance or reactance.

Referring to Figs. l and 2, the problem is to maintain constant, the load voltage V2 across the secondary winding 14, regardless of variations in the voltage V1 across the supply leads 26 and 28. This requires that the magnetic flux in the core of the transformer 12 be main- -tained constant, which in turn requires that a constant voltage E be induced in the primary windings 16 `and 18 of the transformer and another constant voltage be induced in the correcting winding 20. Thus, the problem resolves itself into maintaining the voltage impressed across the primary winding 16 and 18 constant, and equal and `opposed to the induced voltage E, regardless of variations in the supply voltage V1 across the leads 26 and 28.

Referring now to Fig. 2 let us assume that the supply voltage V1 is normal; therefore, if the load voltage V2 is to be normal, it is necessary that the supply voltage V1 equal the induced voltage E.

Assuming that the Voltage induced in the correcting winding 20 is in the direction so that the right-hand end is at a higher potential than the left-hand end thereof, the conductor 52 and the corner 46* of the bridge circuit 3@ will be at a higher Vpotential than the conductor 54 and the corner 44 of bridge circuit. However, if the impedances of all of the reactors 32, 34, 36, and 38 are equal (as shown diagrammatically in Fig. 2), the voltage drops across the reactors 32 and 38 will be the same; and, if they are also in phase, the corners 46 and 42 will be at the same potential, and the adjusting voltage e (which is across the corners 42 and 46) will be zero. The voltage E equals the voltage V1 plus or minus the voltage e, and, inasmuch as the voltage e is zero, the voltage E equals the voltage V1. As mentioned above, the voltage e is Zero provided the voltage drops across the reactors 32 and 38 are equal and in phase. This condition occurs when the current flowing through the windings 16 and 18 is small in comparison with the Conditions are considerably more complicated when this is not correct, as occurs when the transformer carries an appreciable load current. This point will be discussed in more detail hereinafter.

Referring next to Fig. 3, let us assume that the voltage V1 is 110% of normal, and therefore, in order 'for the voltage E to be normal, it is necessary to connect in series with the supply voltage V1, an adjusting voltage e which lopposes or reduces it, or, stating it differently, Vthe Yadjusting vol-tage e must vbe of VSuch magnitude and phase relation with respect to the voltage V1 that the resultant voltage E is of normal value, i.e., less than the supply voltage "lf 1.

Stating it differently, the adjusting voltage e must buck the supply voltage V1 by an amount equal to 10% of normal V1.

As mentioned previously, the voltage induced in the correcting winding is in the direction to cause the corner 40 of the bridge to be at a higher potential than the corner 44. Therefore, when the impedance of the reactors 32 and 36 are considerably less than `the impedance of the reactors 34 and 38 (Fig. 3), the corner 42 will be at a higher potential than the corner 46. Thus, under these conditions, the adjusting voltage e across the corners 42 and 46 will be in the direction opposite `to the supply voltage V1, and the voltage E will equal the voltage V1 minus the voltage e. Consequently, if the voltage V1 is 110% of normal, and Ithe voltage e is 10% of normal V1, the voltage E will be normal, and consequently the load voltage V2 across the secondary winding 14 will also be normal. It will be noted that if the impedances of the reactors 32 and 36 are considerably less than the impedances of the reactors 34 and 38, the voltage e across the corners 42 and 46 of the bridge is substantially equal to the voltage across the leads 54 and 52 of the winding 20.

Referring to Fig. 4, if the voltage V1 is 90% of normal, it is necessary for the adjusting voltage e to be 10% of normal V1 and in the direction to aid it rather than `oppose it as previously described. Thus, if the impedance of the reactors 32 and 36 is greater than the impedance of the reactors 38 and 34, the corner 46 of the bridge will be at a higher potential than the corner 42, and the voltage e across the corners 42 and 46 will aid the impressed voltage V1. Therefore, the Voltage E will equal the voltage V1 (90% of normal) plus the voltage e (10% of normal V1), and the voltage E will be normal.

Up to this point it has been assumed that the voltage drops across the bridge reactors are cophasal. These `conditions were assumed in order to simplify the theoretical explanation of the voltages which result when the current flowing in the primary `of the transformer is small in comparison with the current owing in the reactors. However, in reality, these ccphasal voltage conditions exist only rarely. When the transformer is loaded, the voltages across the different reactors are no longer cophasal and the voltage relations become much more complex. For example, when the four reactances have equal impedance (Fig. 2) and ther load current flowing from the corners 42 and 46 is cophasal with the voltage across the leads 52 and 54, a voltage e appears across the corners 46 and 42 of the bridge, which is approximately at right angles to the voltage across the leads S4 and 52 lof the winding 20, or approx-v imately at right angles to the voltage of E across the windings 16 and 18. ln this case, the voltage E equals the voltage V1 in spite of the fact that a voltage e appears across the corners 46 and 42 of the bridge.

If the values of the reactances are such that the ratio of the reactance of the reactor 34 to the reactor 32, and the ratio Iof the reaotance of the reactor 38 to the reactor 36, is rather small, the voltage e across the corners 46 and 42 of the bridge attains a nearly cophasal relationship with respect to the voltage across the leads 54 and 52 of the correcting winding 20, and with respect to the voltage E across the windings 16 and 18.

Gther and more complex relations occur when the current in the leads 28 and 26 is appreciable in comparison with the current flowing in the leads 54 and 52. These can be readily determined from Fig. 1l which is a vector diagram of the voltages appearing at different parts of the bridge circuit shown in Fig. 2. Fig. 11 also illustrates the currents owing in the circuit when the current in the 6 leads 28 and 26 and the windings 16 and 18 are cophasal with the voltage E across the windings 16 and 18.

The meaning of the different vectors in Fig. ll are as follows:

0-a=current in the conductors 28, 48 and 26 and the windings 16 and 18 0-b=current in the reactor 34 0-c=current in the reactor 32 lt can be shown mathematically that the point 3 as well as point 3 travel on a parabola, provided the sum of the reactances 32 and 34 remain constant and the sum of the reactances 33 and 36 remain constant, while the ratio of the reactances 32 to 34, and 36 to 38 are varied.

The parabola becomes atter as the current flowing in the leads 23 and 26, and in the windings 16 and 18 becomes smaller when compared with the current flowing in the leads 54 and 52 of winding 20. lf the current in' the leads 23 and 26 is very small in comparison with the current in the leads 52 and 54, the parabola becomes a straight line coinciding with the line 0-2 (Fig. 11). When this occurs, the diagram represents the condition considered in the beginning of the discussion, Le., when the magnitude of the load current is negligible in comparison with the current flowing in the reactances. It is evident that vector diagrams of the kind described can be prepared for any desired load condition.

1t will be noted f om Fig. l1 that when the ratio of the reactances Vis changed, the adjusting voltage e across the corners 46 and 42 of the bridge (represented by vector 3-3'), changes in magnitude and phase angle with respect to the voltage across the corners 40 and 44 of the bridge (vector 0 2) and across the leads S4 and 52 of the correcting winding 20.

As mentioned hereinabove, Fig. 12 illustrates the situation wherein the supply voltage V1 is smaller than the voltage E across the terminals of the primary winding of the transformer, and the adjusting voltage e forms the phase angle a with the voltage E.

Fig. 13 illustrates the situation wherein the supply voltage V1 is larger than the voltage E across the primar] winding of the transformer, and the adjusting voltage e forms a phase angle a, with the voltage E, which in turn is cophasal with the voltage across the correcting winding 20.

kFor the extreme case wherein the reactances 32 and 36 are very small, or Zero, the supply voltage V1 must be great enough to create a voltage equal to the primary voltage E plus the voltage e across the correcting winding, a condition which is represented by line 01-2 of Fig. 12. For the other extreme case wherein the reactances 34 and 38 are very small, or zero, the supply voltage is represented by 0-3.

In the above discussion, it was assumed that the end of the vector representing the adjusting voltage e, travels on a parabola. As pointed out hereinabove, this occurs when the sum of the reactances of the reactors 32 and 34 is constant, and the sum of the reactances of the reactors 36 and 38 is constant, while the ratio of the reactances 32 to 34 and the ratio of the reactors 36 to 38 are varied.

Thus, it will be apparent that by varying the impedances of the reactors 32, 34, 36 and 38 (either manually or automatically as described hereinabove) the adjusting Voltage e across the corners 42 and 46 of the bridge is changed in its magnitude and phase relationship with respect to the voltage E across the primary windings 16 and 18 of the transformer, so as to either aid or oppose the supply voltage V1 and thereby maintain constant the voltage V2 across the secondary.

In Like manner, the voltage E across the primary windings 16 and 1S can be made to follow any desired curve or pattern. Y

Furthermore, this correcting of the impressed voltage V1 by varying the voltage e, is accomplished smoothly and practically instantaneously with the demand therefor Fig. 5 is similar to Fig. l and Fig. 2, and has been included to show another way of schematically illustrating the basic circuit.

In the circuit previously described ('Fig. l and Figs. 2-5), the voltage impressed across the corners 4h and 44 of the bridge circuit, i.e., the bridge supply voltage, was obtained from a correcting winding 2i? mounted on the same core with the primary windings 16 and 18 and the secondary winding 14. Also, the adjusting voltage e across the other corners 42 and 46 was superposed on or injected into a power supply lead.

Substantially the same results can be obtained by superposing the adjusting voltage e developed by the bridge circuit, onto the secondary or load side of the transformer whose voltage is to be controlled (Fig. 8). Furthermore, a separate `or auxiliary transformer across either the primary or secondary leads can be used in place or the correcting winding 20, for furnishing the bridge supply voltage.

First, let us consider obtaining the bridge supply voltage from a source other than a correcting winding 2t) mounted on the same core with the windings 16 and 1%.

Referring to Fig. 6, there is provided a main transformer 112 which is equivalent to the main transformer 12 of Fig. 5, and which includes primary windings 116 and 113 and a secondary winding 114. A bridge circuit 13@ complete with four reactors, as previously described, is connected at the corners 142 and 146 into one of the primary leads. The other corners, 14d and 144, are connected to a winding 120, but instead of this correcting winding being on the same core with the windings 116, 113 and 114, it is actually the secondary of the separate transformer T1 which is connected across the output circuit of the transformer 112, i.e., across the leads 124 and 122.

The operation of this circuit is very similar to the one previously described (Fig. 5) in Jthat the impedances of the reactors are varied to provide an adjusting voltage e between the corners 142 and 146 of the bridge, and the voltage e is superposed on the primary voltage to provide the desired voltage across the windings 116 and 118.

If desired, the primary winding of the separate or auxiliary `transformer T1 can be connected across the supply leads 126 and 128 as shown in Fig. 7. The operation of this circuit is closely related to that of Fig. 5.

The present invention also encompasses the construction wherein the adjusting voltage e is superposed on the output voltage of the transformer whose Voltage is to be controlled, as shown in Figs. 8, 9 and l0.

Referring to Fig. 8, there is provided a transformer 212 which contains primary windings 216 and 218, a secondary winding 214, and a correcting winding 220. A bridge control circuit 230 has its corners 242 and 246 connected in the input lead 224 (as distinguished from its Vposition in a primary lead, as in the prior description), and the correcting winding 22@ is connected to the other corners 249 and 244 in a manner previously described.

Thus, the adjusting voltage e developed across the corners 242 and 246, is superposed on the output voltage either to aid or oppose it depending on whether the primary voltage is below or above normal. For example, if the primary voltage V1 is below normal, the adjusting voltage e will 'be controlled by varying the impedances of the reactors (as previously described) so as to aid or increase the secondary voltage V2 and thereby maintain it at its normal or desired value. If, on the other hand, the primary voltage V1 is above normal, then the voltage e will be in the direction lto oppose V2 and hold it down to its normal value. Then again, in those instances where V1 is normal, the impedances of the reactors will be so adjusted that the voltage e will be zero, or have such a phase relationship with respect to the voltages V1 and V2 that these two voltages will be substantially equal.

Referring next to Fig. 9, this circuit combines both the separate power source for the bridge circuit and the superposing of the correcting voltage e on the secondary side of the regulator. In short, it is somewhat similar to both the circuits shown in Figs. 7 and 8. Thus, the corners 342 and 346 of the bridge circuit are connected in an output or load lead, and the other corners 340 and 344 are connected to a winding 320 which is the secondary of a separate transformer T12 connected across the secondary leads ahead of the bridge circuit.

It will be readily apparent that the transformer T12 could be connected on the load side of the bridge circuit, as shown in Fig. 10, if desirable.

The descriptions considered hereinabove were directed to a Wheatstone bridge circuit containing four separate saturable core reactors. It has been determined that a somewhat superior operation is obtained when the two diametrically opposite reactors which comprise a set, are combined into a single twin reactor unit consisting of a single three-legged iron core provided with two A.C. windings and one D.C. winding.

The iron core of each twin reactor has three legs, each of the two outer legs being provided with an A.C. winding, and the inner leg being provided with a single D.C. winding which replaces the two D.C. windings of the two independent reactors.

In addition to providing a `somewhat superior operation, the twin reactors have the further advantage that they require less iron and copper and occupy less space 'than two separate reactors. Also, the twin reactors have a tendency to cause equal current distribution in the 'two A.C. windings.

Thus, it is apparent that there has been provided a novel regulator circuit by which the output voltage of a transformer can be held constant or at any desired voltage, regardless of variations in the supply l-ine voltage. Also, the regulation is accomplished almost instantaneously with the demand thereof, and the adjustment is made smoothly and without interrupting the normal `iow of either the supply current or the load current. In addition, the device is relatively simple in construction and there are no mechanical switches or moving parts to become worn, or out of adjustment.

It is to be understood that the foregoing description and the accompanying drawing have been given only by way of illustration and example, and that changes and alterations in the present disclosure, which will vbe readily apparent to one skilled in the art, are contemplated as within the scope of the present invention which is hunted only by the claims which follow.

What is claimed is:

l. In combination, a pair of supply leads; a Wheatstone type bridge circuit including at least four saturable core reactors connected together to provide two sets of 0pposed corners and two sets of opposed reactors, each set of reactors having at least one D.C. coil associated therewith; a transformer containing a primary winding, a secondary winding, and a correcting winding; a connection between one side of the primary winding and one of the supply leads; a connection between the other side of the primary winding and one corner of one set of corners of the bridge circuit; a connection between the other corner of said set and the other supply lead; and connections between the other set of corners and the correcting winding.

2. In combination, a pair of supply leads; a pair of load leads; a Wheatstone type bridge circuit including at least four saturable core reactors connected together to provide two sets of opposed corners and two sets of opposed reactors, each set of reactors having at least one D.C. coil associated therewith; a first transformer containing a primary winding and a secondary winding; a second transformer containing a primary winding and a secondary winding; a connection between one Side of the primary winding of the rst transformer and one of the supply leads; a connection between the other side of said primary winding of the first transformer and one corner of one set of corners of the bridge circuit; a connection between the other corner of said set of corners and the other supply lead; means connecting the secondary winding of the rst transformer with the load leads; means connecting the primary winding of the second transformer across the secondary winding of the first transformer; and connections between the secondary winding of the second transformer and the other set of corners of the bridge circuit.

3. In combination, a pair of supply leads; a Wheatstone type bridge circuit including at least four saturable core reactors connected together to provide two sets of opposed corners and two sets of opposed reactors, each set of reactors having at least one D.C. coil associated therewith; a first transformer containing a primary winding an a secondary winding; a second transformer containing a primary winding and a secondary winding; a connection between one side of the primary winding of the first transformer and one of the supply leads; a connection between the other side of said primary winding and one corner of one set of corners of the bridge circuit; a connection between the other corner of said set and the other supply lead; means connecting the primary winding of the second transformer across the supply leads; and connections between the secondary winding of the second transformer and the other set of corners of the bridge circuit.

4. In combination, a pair of load leads; a Wheatstone type bridge circuit including at least four saturable core reactors connected together to provide two sets of opposed corners and two sets of opposed reactors, each set of reactors having at least one D.C. coil associated therewith; a transformer containing a primary winding, a secondary winding, and a correcting winding; a connection between one Side of the secondary winding and one load lead; a connection between the other side of the secondary winding and one corner of one set of corners of the bridge circuit; a connection between the other corner of said set and the other load lead; and connections between the correcting winding and the other set of corners of the bridge circuit.

5. In combination, a pair of load leads; a Wheatstone type bridge circuit including at least four saturable core reactors connected together to provide two sets of opposed corners and two sets of opposed reactors, each set of reactors having at least one D.C. coil associated therewith; a first transformer containing a primary winding and a secondary winding; a second transformer containing a primary winding and a secondary winding; means connecting the primary winding of the second transformer across the secondary winding of the first transformer; a connection between one side of the primary winding of the second transformer and one of the load leads; a connection between the other side of said primary winding of the second transformer and one corner of one set of corners of the bridge circuit; a connection between the other load lead and the other of said one set of corners; and connections between the secondary winding of the second transformer and the other set of corners of the bridge circuit.

6. In combination, a pair of load leads; a Wheatstone type bridge circuit including at least four saturable core reactors connected together to provide two sets of opposed corners and two sets of opposed reactors, each set of reactors having at least one D.C. coil associated therewith; a first transformer containing a primary winding and a secondary winding; a second transformer containing a primary winding and a secondary winding; means connecting one side of the secondary winding of the rst transformer with one side of the primary winding of the second transformer and one of said load leads; a connection between the other side of the secondary winding of the first transformer and one corner of one set of corners of the bridge circuit; means connecting the other corner of said set with the other side of the primary winding of the second transformer and the other of said load leads; and connections between the other set of corners of the bridge circuit and the secondary of the second transformer.

7. In combination, a Wheatstone type bridge circuit comprising at least four saturable core reactors connected together .to provide two sets of opposed corners and two sets of opposed reactors; means for impressing a voltage across one set of corners; means for connecting one of the other set of corners with one side of an A.C. power source; means for connecting the other of said other set of corners with one side of an A.C. power output circuit; means for connecting the other side of the power source with the other side of the A.C. power output circuit; and means for Varying the impedance of at least one set of reactors.

8. In combination, A.C. power input and output circuits; a transformer containing at least two windings; a Wheatstone type bridge circuit for providing an A.C. adjusting voltage comprising at least four saturable core reactors connected together to provide two sets of opposed corners and two sets of opposed reactors; means for impressing a voltage across one set of corners; first and second sets of conductors; a connection between one conductor of said first set of conductors and one corner of the other set of corners; a connection between the other corner of said other set of corners and one side of one winding; a connection between the other side of said one winding and the other conductor of said first set of conductors; a connection between one side of the other winding and one conductor of said second set of conductors; a connection between the other side of said other winding and the other conductor of said second set of conductors; means connecting one of said rst and second sets of conductors with said input circuit; means connecting the other of said first and second sets of conductors with said output circuit; and means for varying the impedance of at least one set of reactors.

9. In combination, a power output circuit; an A.C. power input circuit connected to supply A.C. power to the output circuit; a Wheatstone type bridge circuit comprising at least four saturable core reactors connected together to provide two sets of opposed corners and two sets of opposed reactors; means including a correcting winding for impressing a -voltage across one set of corners; means including the other set of corners for coupling said bridge circuit in a series circuit between the power input and output circuits; and means for Varying the impedance of at least one of said reactors.

l0. In combination, power input and output circuits; means for connecting an A.C. supply source to the input circuit for supplying A C. power to the output circuit; a Wheatstone type bridge circuit comprising at least four saturable core reactors connected together to provide two sets of opposed corners and two sets of opposed reactors; transformer winding means for impressing an A.C. voltage across one set of corners; means including the other set of corners for coupling said bridge circuit in a series circuit between the power input and output circuits; and means including a D.C. coil associated with at least one set of reactors for varying the impedance of said one set of reactors.

ll. In combination, an output circuit connected to a load; an input circuit connected to an A.C. power source for supplying A.C. power to the output circuit; a Wheatstone type bridge circuit comprising at least four saturable core reactors connected together to provide two sets of opposed corners and two sets of opposed reactors., each set of reactors having at least one D.C. coil associated therewith; transformer means for impressing a voltage across one set of corners; means including the other set of corners for coupling said bridge circuit in a series circuit between the power input and output circuits; and means for supplying current t0 the D.C. coils of the reactors.

12. in combination, a power loutput circuit connected to a load; an input circuit connected to an A.C. power source for supplying A.C. power to the output circuit; a Wheatstone type bridge circuit comprising two sets of opposed satu-rable core reactors, each set including two A.C. windings 'and a DC. winding, the A.C. windings of the two sets being connected together to provide two sets of opposed bridge corners; transformer means connected to supply an A.C, voltage across one set of bridge corners; means including said other set of bridge corners for coupling said bridge circuit in series between said input and output circuits; means for supplying D.C. current to the D.C. winding of each set of reactors; and means for varying the magnitude of the D.C. current in each of said D.C. windings.

References Cited in the le of this patent UNITED STATES PATENTS 1,824,577 Sorensen Sept. 22, 1931 1,893,760 Boyajian Ian. 10, 1933 1,927,689 Miessner Sept. 19, 1933 2,079,206 Grat et al. May 4, 1937 2,149,092 Kettler Feb. 28, 1939 2,432,399 Edwards Dec. 9, 41947 2,487,697 Conviser Nov. 8, 1949 2,771,579 Ruge Nov. 20, 1956 

